The present invention relates to methods for selectively treating a target site in the body, specifically by changing a temperature thereof, and without significantly affecting other parts of the body.
It is generally known that many disease states and injuries respond favorably to the application of heat and/or cold. For example, hypothermia, i.e. cooling, can reduce blood flow, inflammation and edema, and may alter a variety of effects of ischemia. On the cellular level, hypothermia and hyperthermia (heating) have the ability to effect metabolic and enzymatic activity, reactive oxidant production and gene expression. A number of experimental studies of ischemic stroke have shown that hypothermia reduces the extent of neurologic damage and improves neurologic function.
Prior art methods to effect hypothermia or hyperthermia have a number of disadvantages. Most of these methods primarily involve the entire body by employing surface techniques or systemic intravascular perfusion. U.S. Pat. No. 5,624,392 to Saab and U.S. Pat. No. 6,033,383 to Ginsburg teach the use of heat transfer catheters that are placed into the venous side of the vascular system. These devices cool or heat venous blood passing over them, and the heated or cooled blood is distributed throughout the entire body. Such methods have serious limitations. For example, systemic hypothermia causes shivering, which increases the metabolic rate and may cause serious disturbances of the cardiovascular system. Surface techniques are slow, have limited heating/cooling capability, and require apparatus that can interfere with the ability to perform a medical procedure. In addition, none of these prior art techniques have the ability to control changes in blood flow and pressure that can result from the application of hypothermia or hyperthermia, nor do they have means to administer pharmacologic agents selectively to the target area.
Other prior art methods designed to selectively treat an area without adversely affecting the rest of the body have been disclosed. For example, U.S. Pat. Nos. 6,436,071 and 6,605,106 to Schwartz teach a catheter for intravascular corporeal cooling, designed to eliminate problems that develop due to complications from high pressure within a delivery catheter. This disclosure teaches the use of a pressure relief valve, which has the disadvantage of a likelihood of total body cooling upon activation of the valve. Additionally, long-term effects of the disclosed system can include potential local vascular damage, and additional total body cooling, since arterial blood passing over the cooling catheter would itself be cooled. U.S. Pat. No. 6,042,559 to Dobak teaches a method and apparatus for performing hypothermia without significant effect on surrounding organs or other tissues. The disclosed apparatus includes a flexible supply catheter, and a separate flexible delivery catheter—one used for removing the blood and one used for delivering cooled blood into an artery feeding the selected organ. The delivery catheter has a layer of insulation. However, the use of two catheters increases the risk of vascular complications, the complexity of the procedure, and the time to effect cooling of the target organ.
There is thus a widely recognized need for, and it would be highly advantageous to have, a method for selective thermal treatment which is devoid of the above limitations.